- Title
- A next generation spatially distributed model for soil profile dynamics and pedogenesis
- Creator
- Welivitiya, Welivitiyage Don Dimuth Prasad
- Relation
- University of Newcastle Research Higher Degree Thesis
- Resource Type
- thesis
- Date
- 2017
- Description
- Research Doctorate - Doctor of Philosophy (PhD)
- Description
- Soil is one of the most important resources on planet Earth and soil properties heavily influence various processes in geomorphological, hydrological and climatic systems. Understanding the formation and the global distribution of soil is imperative in the quest for sustainable use of this resource. While spatial characterization of soil properties is important, understanding the evolution of soil properties on a dynamic landform is also crucial. Over the years, various statistical and mechanistic models have been formulated to understand both landform evolution and soil development. However throughout history, soil modelling and landform modelling have developed independent of each other with minimal consideration of the influence of one on the other. In order to fully appreciate the development and evolution of soil on a dynamic landform, coupling landform evolution and pedogenesis is necessary. This thesis tries to address this issue. This work describes the development of State Space Soil Production and Assessment Model (SSSPAM), a soilscape and landform evolution model that integrates soil profile dynamics and landform evolution. First a computationally efficient soil evolution model was formulated by extending the mARM3D modelling framework to explore the soil profile self-organization in space and time, and dynamic evolution. Then the landform evolution was integrated into SSSPAM by incorporating elevation changes incurred due to erosion and deposition. The complexities of physically based process equations were simplified by introducing state-space matrix methodology which allows efficient simulation of mechanistically linked landscape and pedogenesis processes in catena scale spatial extents. The modelling approach and the physics underpinning the modelled processes are described in detail. SSSPAM explicitly describes the particle size grading of the entire soil profile at different soil depths, tracks the sediment grading of the flow, and calculates the elevation difference caused by erosion and deposition at every point in the soilscape at each time step. This allows comprehensive analysis of soil landform interactions and soil self-organization. SSSPAM simulates fluvial erosion, armouring, physical weathering, and sediment deposition. The modular nature of SSSPAM framework allows integration of other pedogenesis processes in follow-on research projects. The pedogenesis module of SSSPAM was first used to explore, through a parametric study, the sensitivity of the area-slope-soil grading relationship first identified by Cohen et al. [2009]. The parametric study confirmed the generality of this area-slope-soil grading relationship and showed that the relationship was present throughout the soil profile. Using the same methodology the dynamics of soil profile evolution on a static hillslope with different depth dependent weathering functions was also studied. This study showed that although the soil surface properties may reach similar equilibrium with different depth dependent weathering functions, the soil profile could be vastly different. Further this study revealed that there are very complex feedback mechanisms which cause different parts of the soil profile to evolve at different rates. Secondly the SSSPAM coupled soil-landscape evolution model was used to study the soilscape development at different spatial scales. First simulations were carried out on a simple synthetic hillslope to understand the relationships between soil characteristics and the geomorphic attributes (slope and contributing area) at the simplest level. Also the process interactions which lead to such relationships were identified. The influence of the depth dependent weathering function and the influence of climatic fluctuation on soilscape evolution were explored. These simulations show that the balance between erosion rate and sediment load in the flow accounts for the variability in spatial soil characteristics while the depth dependent weathering function and climate have major influences in soil formation and evolution. With the insights gained from the simple hillslope soilscape simulations, a series of three-dimensional catena scale simulations were done. The first set of simulation concentrated on studying the evolution of a fluvial fan structure using a synthetic landform. During the simulation SSSPAM was able to mimic “fan head trenching” which is known as the primary process in fan formation. The simulated fan exhibited the same spatial trends in sediment grading and geomorphology that are frequently observed in natural fan formations in the field. This provides confidence in the model. The second three-dimensional simulations used a natural sub catchment belonging to Tin Camp Creek located in Northern Territory, Australia. Field rock content data collected from two transects in the same landform were compared with simulations. The simulated results revealed that the catchment is weathering-limited and showed significant relationships between soil properties and geomorphic attributes. Further, the simulated rock content data trends were comparable with the trends observed in the field. A final set of three-dimensional simulations were done to assess the evolution of an engineered landform. The landform used for this simulation was the proposed ERARM post-mining landform for Ranger Uranium Mine rehabilitation located in Northern Territory, Australia. The simulation results agreed well with previous landform stability assessment studies. The landform was found to be weathering-limited in some places and transport-limited in other regions. The relationships between soil properties and geomorphic attributes were observed in low contributing area regions although these relationships were not as clear as the natural catchment simulation, likely due to the non-natural engineered geomorphology. In summary SSSPAM has demonstrated its potential as a coupled soilscape and landform evolution model. It provides an intellectual and computational basis for understanding soil catena processes, feedbacks with climate, and soilscape spatial organisation.
- Subject
- pedogenesis; soil evolution model; landform evolution model
- Identifier
- http://hdl.handle.net/1959.13/1335875
- Identifier
- uon:27506
- Rights
- Copyright 2017 Welivitiyage Don Dimuth Prasad Welivitiya
- Language
- eng
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